In particular, the present invention is directed to crimping synthetic filament yarns in a false twist crimping machine wherein heating devices are provided to advance a yarn therethrough in a heated groove. The heating device according to the present invention may comprise several grooves, each of which accommodates one yarn.
A prior art heating device is described in EP 0 412 429 B1 and U.S. Pat. No. 5,148,666 wherein the heating device includes a heated groove in which the yarn is guided along a zigzag line. The zigzag line is defined by several yarn guides, each constituting a turning point of the line accommodating one yarn guide.
Prior art heaters are operated at a temperature which is substantially higher than 300.degree. C. At these temperatures, a portion of the organic compounds of the yarn evaporates, whereas anorganic compounds deposit on the yarn guides. These deposits occur because the yarn comes into contact with the surface of each yarn guide. These deposits increase after repeated use. An increase in the deposits causes the yarn to no longer be urged to follow a predetermined path. However, the yarn path in the heater influences the quality of the yarn. Accordingly, the quality of the yarn can be influenced by the deposits.
The structural design of prior art heaters renders cleaning of the individual yarn guides relatively expensive. In addition, the deposits are very hard due to the temperatures in the heater, and they are difficult to remove from the yarn guides.